1. Field of the Inventive Concept
The present inventive concept relates to methods of driving a memory.
2. Description of the Related Art
Memory devices generally include volatile memory devices and nonvolatile memory devices. Volatile memory devices may lose data when the power supply is turned off, while nonvolatile memory devices may retain data for some period of time even when the power supply is turned off. Examples of the nonvolatile memory devices include read-only memories (ROMs), electrically erasable programmable read-only memories (EEPROMs), and flash memories.
Endurance and retention are concepts that relate to data integrity in a memory device. Endurance concerns the number of program/erase (P/E) cycles that a memory device can endure while storing data reliably, and retention relates to the length of time for which data can be reliably stored.
A reduction in geometry and/or an increase in the number of levels per memory cell affect endurance and/or retention. For example, while a single-level cell NAND flash memory can guarantee 100,000 P/E cycles, a multi-level cell NAND flash memory may guarantee only 10,000 P/E cycles.
The most destructive operation in a NAND flash memory is the block erase operation. In a block erase operation, for example, a very high negative voltage may be applied to a bulk contact of the memory device, and a control gate may be maintained at a voltage of zero. Accordingly, electric charge stored in a floating gate may be removed.